This invention relates to a measuring system using a magnetic scale and, more particularly, to a mounting mechanism for mounting the measuring system on a machine tool, for instance.
As is well known in the art, a measuring system using a magnetic scale has been utilized in various fields due to its high accuracy of measurement, and recently it is extensively used in the fields of automatic control. This type of measuring system is actively applied to machine tools from the standpoint of the accuracy of machining works.
Usually, a measuring system using a magnetic scale is mounted on a machine tool in the manner as shown in FIGS. 1 and 2. Referring to FIGS. 1 and 2, reference numeral 11 designates a machine tool body, e.g., a cutter. A movable member 12 with a cutting blade (not shown) is supported on top 11a of the machine tool body 11 such that it can be moved in the directions of arrows A and B. Reference numeral 13 designates a work holder, to which a workpiece (not shown) is secured.
A magnetic head support 14 is coupled at one end to the movable member 12. To the other end of the magnetic head support 14 is coupled a magnetic head support frame 16, in which a magnetic head 15 of the known type is provided. The magnetic head 15 is a flux-sensitive multi-gap head. The multi-gap head consists of a plurality of (usually about 30) single-gap heads arranged in a row at a pitch of .lambda.m/2 (.lambda. being referred to as the specific wavelength of the multi-gap head, and m being an integer) such that they are electrically connected in series, each having a polarity opposite to that of either adjacent single-gap head.
A magnetic scale support 17 is secured by a screw 18 to the machine tool body 11. The magnetic scale support 17 is a hollow angular elongated member having substantially a rectangular sectional profile. A magnetic scale bar 19 is provided in the magnetic scale support 17. The magnetic scale bar 19 is a straight magnetic medium bar, for instance made of a Fe-Co alloy. It has a sinusoidal magnetization pattern having a regular pitch. Its opposite ends are secured by securement members 20 to the magnetic scale support 17.
As shown in FIG. 3, the magnetic head 15 is accommodated in the magnetic head support frame 16 coupled to an end of the magnetic head support 14. The magnetic head 15 has a see-through hole 15a, which is slightly greater in sectional size than, and loosely penetrated by, the magnetic scale bar 19.
When the movable member 12 is moved, the magnetic head 15 is moved along the magnetic scale bar 19, and the magnetic head 15 provides a signal corresponding to the extent of movement of the movable member 12. The signal obtained from the magnetic head 15 is coupled to a signal processing circuit and a digital display unit or the like (not shown) through a cable 21 extending along the magnetic head support 14, so that the extent of movement of the movable member 12 is displayed on the display unit.
The above prior art mounting mechanism for mounting the measuring system on the machine tool, however, has a problem. That is, since the movable member 12 of the machine tool 11 is moved straight in horizontal directions, i.e., directions of arrows A and B in FIG. 1, the magnetic scale 19 has to be installed such that it extends accurately parallel to the direction of movement of the movable member 12.
In the prior art, a dial gauge is installed on the movable member 12 of the machine tool 11 for determining the position of a reference plane of the magnetic scale support 17 and adjusting the magnetic scale bar 19 such that it is parallel with the direction of movement of the movable member 12. This adjustment, however, requires a high precision that the parallelness error of the magnetic scale bar 19 with the direction of movement of the movable member 12 is held within approximately 0.1 mm. The adjusting operation, therefore, is difficult and time-consuming.